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THE EVOLUTION  OF THE PRIMATES      325
whose remains were found in a cave in Madagascar, was truly gigantic, it was about as large as a donkey, and its mode of life was possibly aquatic. The orbits are surrounded by bony rims, which are prolonged outwards, the zygomata are strong and the sagittal crest is low. The mandibular rami are large, and Forsyth Major thought that the animal might have had an air-sac like the Howler Monkeys. The lower incisor teeth are procumbent, and the canine teeth are not large when compared with the size of the skull.
The European Eocene Tarsioids, whose remains have been found in France and Switzerland, can be arranged in several genera, the most notable of which are Necrolemur, Microch&rus, Nannopitliex and Pseudo-loris. Of these Pseudoloris is very primitive, Necrolemur and Microcliaerus are highly specialized, and NannopitJiex is an intermediate form. In Necrolemur the cranial cavity is large, and the large orbits, which are only separated by a narrow partition as in the modern Tarsius, communicate with the temporal fossae behind post-orbital bars and incomplete orbital walls. The lachrymal ducts open on the face, and the tympanic bullse have external auditory tubes. Forsyth Major and Gregory consider that Microcli&rus and Necrolemur are related to the Galagidae.
It is generally believed that all Monkeys were evolved from a common Tarsioid stock; and the most primitive forms first appeared somewhere near America in Eocene times. The actual Tarsioid ancestor has not yet been discovered, however. Some of these early Monkeys migrated to South America where they developed in different ways into the various kinds of PiatyrrhinL